Wave signaling system



Sept- 15- 1936 J.- F. FARRmG-roN 2,054,412,

' WAVE SIGNALING SYSTEM l Filed May 7, 1935 4 sheets-sheet 1 ATTORNEY 512121915, 1936- J. F. FARRINGTON WAVE SIGNALING SYSTEM Filed May '7, 1955 4 sheets-sheet 3 INVENTOR J5? EFA/ww G70/v BY ATTORNEY Sept- 15, 1936. J. F. FARRINGTON 2,054,412

WAVE SIGNALING SYSTEM Y n Filed May '7, 1935 4 Sheets-Sheel'l 4 7f3 A YINVENTOR v J/ FA /54 53 /52 A ,54 f5.5 B N; RR H da,

A'ITCRNEY 'Parental sept. 15, 193s 0 PATENT oFFicE 2,054,412 WAVE SIGNALTNG SYSTEM John F. Farrington, Flushing, N. Y.; assignor to Hazeltine Corporation, a corporation ofDela- Ware Application May i, 1935, sel-iai No. 20,197

42 Claims.

rier frequency of the band passed for controllingl the character of reception. The manipulation of the system is such as to select and pass a relatively narrow frequency band in the process of station selection in order to sharpen the tuning to the carrier frequency. Thereafter and without disturbing the tuning of the system to the reception frequency carrier, the resonance band width may be expanded symmetrically about the carrier frequency of a modulated carrier wave in order to select both of its sidebands equally, thereby to secure double sideband reception thevdelity of reproduction of which is improved in proportion to the expansion of the resonance band. Alternatively the resonance band may be expanded unsymmetrically from the sharp tuning adjustment to select more of one sideband Athan of the other-thereby to provide either upper or lower sideband reception wherein` fidelity of reproduction again increases in proportion to the degree of expansion.

A broad feature of the invention, therefore, resides, in expanding band selectors of the symmetrical and unsymmetrical type in which tuned circuits are reactively coupled to form the band selector and adjustable reactance means are provided for symmetrical and unsymmetricalV expansion.

Radio broadcast signals are ordinarily transl (Cl. Z50-20) ing on adjacent channels, particularly when the interfering signals from said stations are intercepted at the receiving antennawtih a strength comparable to or exceeding that of the desired station. In addition to interfering signals, static and other so-called background noise may prevent undisturbed, i. e., quiet, reception of station selected.

Quiet operation in the presence of interference may be secured by increasing the selectivity, that is, by contracting the resonance band, to prevent appreciable reproduction of the interfering signals and noise. Increasing the selectivity or narrowing the selected band, however, tends to limpair the fidelity of signal reproduction, since the sideband frequencies corresponding to the higher audio frequencies of modulation are suppressed. It is desirable therefore that the selected band width be made narrow only when excessive interference or noise is present, but in its absence, the band width should be adjusted freely to admit and pass all sideband frequencies required for faithful reproduction of the received signals. Y

Either of two methods may be employed foraltering the selectivity to the ends stated. One method comprises expanding or contracting the resonance band symmetrically with reference to the carrier frequency thereby to transmit the carrier and a selected-portion of both sidebands. The other method is that of expanding the resonance band unsymmetrically to one side or the futher of the carrier to receive and reproduce sig-v nals constituting a desired fraction of but one sideband and the carrier. The preferred method of selection depends on conditions of reception in a particular instance.

symmetrical expansion is generally preferable for ease and accuracy in tuning to a selected sta.

tion, because fidelity is not a critical function of tuning. Also when the signal is subject to like interference or noise on both sidebands, sym# l metrical expansion produces less interference relative to the signal. On the other hand, when the desired signal is subject to major interference only onone sideband of the selected station such as that nearest in frequency to the carrier of an interfering station, the unsymmetrical or single sideband expansion is of considerable advantage in that selection of the sideband remote from thev interfering station greatly reduces its interfering effect.

As applied to a superheterodyne receiver in accordance with a preferred embodiment, the invention provides a plurality of tunable reception liliA frequency circuits and a plurality of tuned intermediate-frequency band selectors. Each tuned intermediate-frequency selector is formed of a plurality of resonant circuits preferably coupled adjustably' both inductively and capacitively. Tuning to a desired station is effected by variation of the reception frequency selectors. Expansion of the resonance band for upper, lower, or double sideband reception in a degree desired, is accomplished in the tuned intermediate-frequency selectors, preferably by adjustment of lthe inductive and capacitive couplings. "Thus for symmetrical double sideband ,expansion the inductive coupling alone may be varied; for unsymmetrical or single sideband expansion the capacitive couplings alone may be varied; while suitable variation` of both couplings as explained below serves to sharpeny the tuning to the inter# mediate frequency. v

A feature of the invention resides in the novel mechanical construction disclosed for adjusting the selective properties of the receiver as dired.

' The essence of the construction resides in the use of a control mechanism operable in two degrees of freedom, as for example a shaft capable of rotation and axial displacement. Adjustment in one degree of freedom, is reserved for double sideband expansion, as for example, by utilizing axial displacement of the vcontrol shaft to vary only the inductive couplings in the tuned selectors. Adjustment of the control mechanism in a second degree of freedom may be utilized for single sideband expansion, as by rotation of the shaft to vary only the capacitive couplings in the tuned selectors. y

The control mechanism maybe so arranged that adjustment thereof to a certain limiting position or to a particular setting common to both.

degrees of freedom, so relates the mentioned inductive and capacitive couplings as to sharpen the tuning of the tuned selectors to the inter' mediate frequency preparatory to adjusting the reception frequency .selectors for station selection. The mechanical construction is such, in

accordancey with a further feature of the inven` tion, that only for this particular setting of the control mechanism can the reception frequency selectors be manipulated for tuning.

In the drawings: 'Y

Fig. 1 is a circuit diagram of a selector connected in accordance with the present invention as employed to couple successive amplifier tubes in the intermediate-frequency portion of a superheterodyne receiver.

Figs. 2 and 3 are performance graphs musi 4 trating the selectivity adjustments of which the 6 coupling system.

Fig. 9 is a composite circuit diagram and mechanical assemblyy illustrative of the manner in whichthe mentioned tuning and selectivity adjustments are eifected in accordance with one embodiment of the invention. Fig. 10 shows in plan view a component of the mechanical assembly as sectioned along 9-8 of- Fig. 9: .while Fig. 111s a section along ii-ii of Fig. 9.

Figs. 12 to i7, inclusive, illustrate the mechanical features of an alternative embodiment of the invention. Fig. 12 is a side elevation of the assembled apparatus. Figs. 13 to 415, inclusive, are sections taken along lines i3-|3, i4-I4 and iS-i 5, respectively, of Fig. 12. Fig. 16 is a perspective view of a component of the Figs. 12 and 13 assembly. Fig. 17 is an elevation of the control panel illustrating the arrangement of the tuning and selectivity controls.

Referring to Fig. 1, a tuned band selector T couples thev output of a vacuum tube i to the input of a succeeding vacuum tube 2. The selector comprises a pair of similar, singly resonant circuits 3 and 4 each containing a coil L tuned by a shunt condenser C to a selected frequency. Coil L of the secondary circuit 4 is axially adjustable with respect to coil L of the primary circuit 3 (as indicated by the double pointed arrow) for the purpose of varying the shunt inductive coupling M between the circuits. An adjustable condenser E is connected between the uppert terminals of the condensers C in circuits 3 and 4 to provide a variableseries capacitive coupling between' these circuits.

Signals are selectively relayed from tube i through the selector T to tube 2 by connection of primary circuit 3 between the anode 5 of,

tube i and ground 6 through the plate supply battery 1. To complete the output circuit of tube i, its cathode 8 is grounded through a grid biasing impedance 9. Secondary circuit 4 is connected between the signal control grid i of tube 2` and ground. The grid circuit of tube 2 is completed by connecting its cathode ii to ground through a grid biasing impedance I2.

As a circuit refinement, selector T may be terminated to ground in an adjustable resistance -P, and switching means il and I4 may be arranged to shunt condenser E with a resistance R, in series with a blocking condenser F, to control the selectivity characteristics of the .system in a manner explained below.

Coil L of circuit l is so poled with respect to coil L of circuit 4 that the inductive coupling M opposes the capacitive coupling E. When the capacitive coupling due to E is adjusted substantially to annul the inductive coupling M at a selected frequency, the eiective coupling between circuits 3 and 4 will be so small as to provide a single humped highly selective resonance characteristic for selector T such as is obtained with less than optimum coupling. Although the resultant coupling is low for these adjustments it is not zero owing to a small resistance component probably in the mutual inductance branch. Curve a of Fig. 2 graphically illustrates this condition, optimum response be- `ing obtained at a desired frequency which in this case is 175 kilocycles.

If, starting from this condition, the capacitance of condenser E is decreased, the coupling between circuits 3 and 4 will increase due to the increasing preponderance of Athe inductive over the capacitive coupling from the condition of balance andthe resonance band width ofthe selector lower frequencies as shown by curves a to e to y. It will be observed that'this shifting of the center of the resonance band is accompanied by no diminution, but on the contrary by an increase, in the response at frequency f as compared to that at the point of minimum coupling, curve a.

The character of selectivity variation effected by adjustment only of the capacitive coupling E is ideal for single sideband reception because band width expansion is achieved by maintaining one limit of cut-oir substantially fixed to include the carrier frequency, the other limit being variable to include a desired portion of the upper or lower. sideband. The limits of adjustment of condenser E are such as to include the entire sideband as illustrated by curves c and g. To this lend the maximum capacitance of the condenser E is of such a magnitude that the coupling provided thereby is of the order of twice the normal inductive coupling M. If, as thes limiting adjustments are approached, peaks vin the resonance curve become prominent enough to introduce signal distortion, they may be attened to provide substantial uniformity of response within the transmitted band by terminating the coupling systemin resistance, such as P, ad-` justed to a proper magnitude. In general it is sufficient to terminate the output of the selector in a resistance P, although a second resistance may be similarly connected across its input.

If for the condition of minimum coupling the response, curve a, is too low at the frequency f, it may be improved by shunting condenser E by a suitably chosen high resistor R. The resistor should, however, be disconnected-as by opening switches I3 and I4, for all coupling adjustments providing expanded selection.

It will be noted that the yunsymmetrical expansion for single sideband selection is procured by alteration of the mean frequency of the selector circuits 3 and 4 by changing the self reactance of these circuits by adjusting the condenser E, which at the same time vvaries the' coupling reactance between them.

In order to expand the resonance band Sym` metrically with respect to the carrier frequency f to secure double sideband reception, the capacitive coupling E is maintained fixed at the value corresponding ,to curve a, and the inductive coupling y M increased, for example, by moving coil L of secondary circuit 4 toward coil L of the primary circuit 3. Fig. 3 illustrates the effect on selectivity of such expansion. Curve his for a partial expansion and curve i for an expansion sumcient to include the carrier frequency and all of the two sidebands. The rather prominent resonant peaks of curve i may be flattened by adjustment of resistance P to provide the substantially uniform response of curve i within the transmitted range.

'Ihe selector T may be adjusted initially for single or double sideband selection at frequency f by disconnecting condenser E and tuning cir-'- cuits 3 and 4 to a frequency higher than f and such that, with the mutual inductance M adjusted to provide a resonance band equal in width to both signal sidebands. the lower resonance peak will be allocated atfrequency f as shown by curve k of Fig. 2.

The circuit of selector T, Fig. 1, is basically that of Fig.- 4, wherein resonant circuits .3 and 4 are composed of condensers C shuntedl by coils of inductance L mutually coupled inductlvely to provide series arms of lnductanceL-M and a shunt arm of inductance M.. The capacitive, cou- From the above, it will be seen that, for syml metrical expansion, the mutual reactance between the two tuned circuits is adjusted without affecting the self-reactance or tuning of either circuit.

For unsymmetrical expansion, on the other hand, both the mutual reactance and the selfreactance, or tuning, of the two tuned circuits are simultaneously adjusted. In this latter case, the circuits-may conveniently have a iixed mutual reactance of a given type and an auxiliary mutual reactance of the opposite type or phase and variable between appropriate limits greater and less than the xed mutual reactance, the former serving to vary also the self-reactance, or tuning, of the circuits.

Fig. 5 is a modied circuit accomplishing the same general results as those of Figs. 1 and 4. The change to the circuit of Fig. 5 consists merely in connecting the condenser E in series with the mutual inductance' M rather than across the series arms L-M as in Fig. 4. Thesizes of conldenser E in the two types of selectors are generally quite different, however.

tube coupling as shown in Fig. 6. Coils L, relatively adjustable axially for varying the mutual inductance M, are connected in series between the plate I5 of tube I6 and the signal control grid I`I of tube I8.v From the point between coils L the coupling condenser E is connected to ground. The resonant circuits I9 and 20 are formed by connecting condensers C to ground from the plate and grid leads, respectively, of tubes I6 and I8.

Plate current is supplied to tube I6 from grounded battery 2| through ahigh-frequency choke coil 22 and coil L of resonant circuit I3, the cathode 23 of tube I6 being grounded through the biasing impedance 24 to complete the circuit.

In order to isolate battery 2I from the grid I'I of tube I8, a blocking condenser 2 5 is interposed in the grid lead. This necessitates grounding grid I1 through a leak resistor 26, which may also serve as a compromise terminating impedance for the selector. The cathode 21 of tube I8 is grounded through impedance 28 to complete the input circuit to tube I8. y

Figs. '1 and 8 show the selectivity performance of the Fig. 6 selector T. Fig. `'7 represents the eil'ect of varying only the capacitive coupling E, and Fig. 8 that due to variation only of the inductive coupling M. The selector is adjusted for single or double sideband expansion-with respect to a selected frequency f by tuning circuits I9 and 20 by means of condensers C and with condenser E shorted, to a frequency somewhat below frequency f, and such that adjustment of the mutual inductance M for considerably over-optimum coupling will allocate the upper resonance peak at frequency f. Upon removal of the short circuit, condenser E is adjusted in relation to the thus established inductive coupling to secure minimum eective coupling at frequency f. Due to the fact that the capacitive couplingE and the inductive coupling M are effectively in series they will oppose and thereby'substantially annul one another to provide this minimum coupling.

The frequency-response characteristic 'of the selector for the minimum coupling adjustment is shown by curve l of Fig. 7. Starting from this response the selectivity is varied to provide single sideband selection by adjustment of condenser E. Decreasing the capacity of E to a properly selected limit will result in the upper sidebandselec- 4 tion of curve m.while increasing E from the initial setting will shift the center of the resonance curve toward the lower frequencies while broadening the response until a desired maximum expansion characteristic, such as is depicted by curve n, is

sharp dip in curve l may, for this selectivity adjustment only, be minimized by shunting condenser E with a resistor of appropriate value.

Fig. 9 is the circuit diagram of a complete radio receiving system employing a plurality of tuned expanding band selectors in accordance with the invention. The receiver, of the superheterodyne type, utilizes the tuned selectors as intertube cou- K plings in the intermediate-frequency portion. Manipulation of such a receiver entails: 1) 'simultaneously adju'stng all tuning elements in the radio-frequency portion o'f the system for tuning to the reception frequency; like adjustments of the several tuned selectors to provide either (2) single sideband or (3) double sideband reception of a desired selectivity; and by way of optionally included refinement, (4) inclusion at the proper point in the manipulation cycle of suitable selectivity determining resistors, such as R and P of Fig. 1. l'I'he desirability is apparent'of having all of these adjustments carried out by a simplified control. The mechanical construction of such a control in relation to the circuit manipulation is likewise included in the Fig. 9 showing.

In the circuit of Fig. 9, the antenna-ground circuit 48, 4i is transformerv4 coupled to a double tuned preselector 42 comprising resonant circuits 43, 44 tuned by condensers 45, 46, respectively, and compound coupled in aiding phase relation by mutual inductance 41 and capacity 48. Selector 42 applies the selected signals to the grid circuit of a stage of radio-frequency amplification, tube 48, the amplified signals fromwhich are relayed to a modulator, tube 58, through a selector Il comprising a transformer having a secondary tuned by a variable condenser 52. The modulator cathode 53 is-.grounded at 54 through a biasing impedance 55 and the secondary coil of a transformer 56 the primary of which serves reactively to couple the electrodes of an oscillator tube 51 for generating hetercdyne oscillations of a frequency determined by the setting of` a condenser 58 tapped in series with a fixed condenser 58 across abortion of the transformer primary. e Hetero- 'dyne oscillations from the source, tube 51, are

thus applied to the modulator tube 58 along with the signaling frequencies relayed through selector 5 i. A signal derived bias voltage from some point of the system may be applied to the point AVC for 65 of Fig. 1, relays the modulated intermediate- Afrequency signals from the modulator, tube 58, to' a stage of intermediate-frequency amplification, tube 8|. A similar band selector 62 relays the amplified intermediate-frequency modulated signals to a detector, tube 88, to the output of which is coupled an audio-frequency ampliiier, indicated schematically by rectangle 84, and thence to a loud speaker 85.

The functions of tuning and selectivity adjustment are controlled by the mechanism shownin v the lower portion of theldrawings. The. mechanism includes a control shaft 18 operable in two degrees of freedom. The shaft is -axially displaceable between limiting positions, and rotatable by a control-knob 1I aillxed to the shaft terminus. The shaft is provided with a transversely projecting pin 12 adapted upon adjustment of the shaft to one linut of axial displacement to mesh with the peripherally serrated collar 13. Shaft 18 is not in contact with collar 13 which is free to rotate in. bearings 14 of support 18 aiilxed to the frame or chassis 16. vAdjustment of shaft 10 to the opposite linut of axial displacement causes pin 12 to mesh the peripheral teeth of a second collar 11, likewise not contacting with shaft 18 but free to rotate in bearings 18 of supports 18. The pin 1-2 and collars 13 and 11 thus constitute a selective clutch mechanism whereby rotation of the control knob 1I at one limit of axial displacement rotates collar 11, whereas at the opposite limit of axial displace ent knob 1I is rotatable to rotate sleeve 13. Ieto collar 13 is a pulley 88 carrying a belt c drives a pulley 82 keyed to the shaft 83 of a rotary gang condenser indicated at 84. The gang condenser, the structural details of which are not shown because well known, comprises the tuning condensers 45, 46, 52 and 58 in the radio-frequency portion of the system. Accordingly, adjustment of the gang condenser 84 by the mentioned manipulation of knob 1| t'o ro- K tate collar 13 will simultaneously vary all the condensers mentioned to adjust the radio-fredrives a-gear 81 keyed to shaft 88 rotatably supported by brackets 18. Shaft 88 drives through bevelled gears 88 and 88 a shaft 8| on vwhich` are mounted the rotor elements of the coupling condensers E in selectors-88 and 82. Therefore rotation of knob 1l, when the shaft 18is axially displaced to engage pin 12 with collar 11, adjusts the intermediate-frequency portion of the system for vupper or lower sideband selection in the manner described in connection with Figs. 1 and 2. Moreover, this selectivity adjustment is accomplished without disturbing the tuning adj ment because pin 12 is n ow disengaged from sl eve 18.

When it is desired to tune the radio-frequency portionof the system itis important that condensers E of selectors 68 and 62 shall be at their mid-setting.4 To accomplish this automatically as shaft 18 is displaced tothe left to engage the tuning control 12, 13 a centering mechanism is provided. For this purpose there is keyed to shaft 18 a flanged collar'82 which continuously engages a peripheral slot 83 in a sleeve member `84 axially displaceable on a shaft 88 affixed byv means of nuts 86 to the frame 18. Pin 81 passing through sleeve 84 and across a fiat'portion of shaft 85 prevents rotation of the sleeve on' the iso that rotation of the tuning control shaft |32 will operate the gang 'tuning condenser |30.

Double and single sideband selectivity adjustment is regulated by the expander shaft |36. This shaft is axially displaceable without rotation between limiting positions, and is rotatable Without axial displacement only in the one limiting position illustrated in the drawings, that is, when pushed in to maximum extent. In the'position illustrated in the drawings, shafty |36 is capable of rotation plus and minus 90 from a mid-position to adjust the selectivity for single sideband reception by operation of the coupling condensers E of selectors |44 and 45 in the intermediatefrequency portion of a receiver, such as is illustrated in Fig. 9 and repeated in Fig. l2. The mechanical connection between the expander shaft |36 and the shaft of condensers E in 'gang assembly, is through the sliding coupling |46 and the shaft |41, which may be a solid or exible shaft depending on the relative locations of shaft |36 and the rotor shaft of the gang `assembly vof condensers E. This mechanical coupling is indicated diagrammatically by the dashed line |48. Indicatorpointer |50, Fig. 17, may be carried on shaft |36 to show the amount of single sideband l expansion and'whether the upper or lower sideband is being received. The full in position of shaft |36, also adjusts the mutual inductance couplings M of selectors |44 and M5 to the correct' value, curve a, Fig. 2, for single sideband operation, by mechanical control of the position of the secondary coils L with respect to the associated coils L.

For double sideband expansion controlA shaft |36 must be rotated to the mid-position, thus correctly setting the couplingA condensers E in relation to the mutual inductive couplings M to provide minimum effective coupling or maximum selectivity according to curve a, Fig. 2, after which shaft i36 may be vwithdrawn but not rotated, to increase only the inductive couplings M for double sideband selection in the manner explained above in connection with Fig. 9. The sliding coupling |46 permits of axial translation without rotation of shaft |36, thus maintaining -condensers E fixed at the mid-position.

The expander control is constrained to follow the paths described, for single or double sideband selection, by reasonof blocks 15| aflixed to bracket |52 and separated the width of pin |31. When shaft |36 is pushed in to the maximum extent, pin |31 clears blocks 15| and is thus .rotatable to adjust condensers E for single sideband selection. In order to expand the resonance band for double sideband selection, shaft |36 must be rotated to its mid-position toalign pin |31 with the passage between blocks |5| thereby to permit axial displacement of shaft |36.

The lower portion of pin |31 is transversely displaceable Within a slot |53 of a block |54 provided with grooves |55 for slideably supporting block |54 on spaced guides |56 paralleling shaft |36 and terminating in bracket' |51. Bracket |52 is cut away as indicated at |58 to permit passage of block |54.

A shaft 159,-mechanically coupled as indicated at |60 to the secondary coils L of the selectors,

, is slideably supported, parallelto shaft |36, by

|36 is in its mid-position of rotation. This brings the upper portion of pin |31 in line with the space between blocks |5| and also' in line with a corresponding slot, Fig. 14, in bracket |52 so that the pin may pass through. The initial and final positions of the secondary coils L withv respect to the primary coils L are determined by the permissible travel of block |54 between brackets |51 and I6 These limiting positions are so arranged thatthe limited travel of block |54 will cause the desired change in the mutual inductances M. The pins |56 serve additionally to prevent rotation of shaft |36 during double sideband expansion by constraining the lower portion of pin |31 to travel between them. Scale |49, on shaft |36, indicates vthe degree of double sideband expansion.

It was suggested in the description of the Fig. 9 assembly, especially in double sideband expansion, that it might be desirable to terminate selectors |44 and |45 in adjustable resistances P to smooth out the double peaks in the resonancel curve `due to over-optimum coupling in the expanded condition. In the system of Fig. l2 this is accomplished by mechanically coupling the sliders of resistances P to shaft |59 as is indicated by the dashed lines |53.

modulation and frequency transposition type to attain control of the character of the waves finally radiated, i. e., whether they are double or singlev sideband with carrier and regulate the amount of sideband width. Such application is important particularly in short wave-signaling.

What is claimed is:

1. In a modulated carrier wave signaling system, a resonant band selector, a first means for expanding the resonance band of said selector symmetrically about the carrier frequency of a modulated carrier wave to select both of its sidebands equally, and a second means for expandingsaid .resonance band unsymmetrically with respect to said carrier to select more of one sideband than of the other. 4

2. In a modulated carrier wave signaling system, a resonant band selector, a rst means for continuously expanding the resonance band of said selector symmetrically about the carrier -frequency of a modulated carrier wave to select both of its sidebands equally, and a second means for continuously expanding said resonance band unsymmetrically with respect to said carrier to select more of one sideband than of the other.

3. In a modulated carrier wave signaling system, a resonant band selector, a rst means for expanding the resonance band of said selector symmetrically about the carrier frequency of a modulated carrier wave to select both of the sidebands equally, and a second means for expanding said resonance band unsymmetrically in either direction with respect to said carrier to selectA more of either sideband than of the other.

4. In a modulated carrier wave signaling system, a resonant band selector, a first means for continuously expanding the resonance band of said selector symmetrically about the carrierfrequency of a modulated carrier wave to select both of its sidebands equally, and a second means for 'with reference to Fig. 1.

spaans i rig. 10. Projecting between the-tapered guides |00 and |0| of the yoke is a pin 99 afllxed to the shaft 98 which controls the adjustment of condensers E in selector and 92.

If single sideband expansion has been in use, slide 94 will have been pulled to its extreme right-hand limit and pin 99 may be in anyposition between guides |00, |0| of yoke 99. If now it is desired to tune in another station, knob 1| must be displaced furthest to the left to engage the tuning control.- This forces yoke 99 to the left thus causing pin 99 to come to center between guides |00, |0| in the narrow section at the neck of the yoke thereby automatically centering condensers E.

To obtain double sideband expansion shaft 10 must be in the tuning position with clutch 12, 13 engaged and condensers E centered as described. The mechanism forV effecting double sideband selection includes a flanged collar |02 keyed to the shaft 10 and adapted to engage -a slot |03 in a sleeve |04 which is keyed, by means of a pin |05, to a square shaft |06 and which is vertically displaceable on the shaft |09, as

shown'in Fig. 11, to permit flange |02 to disen-` gage the slot |03. 'I'he engagement and disengagement is eilected by means of a cam |01 keyed to a shaft |08 which is operable by a knob |09. The cam is provided with a curved outer edge eccentric to the axis of shaft |08, so that rotation of the shaft to displace the cam |01 between stops |09 and ||0 raises or lowers sleeve |04.

Shaft |09, supported by bracket affixed to the frame 16, is axially displaceable correspond-v ingly to displace a shaft I2 in which shaft |09 is terminated. Shaft I2 is mechanically connected to the movable secondary coils L of selectors 60 and 62, as indicated by the dashed lines H3, axially to displace the movable coils relative to the fixed coils L in these selectors, thereby to vary the inductive coupling between coupled resonant circuits of the selectors in the manner 'described or flexible depending on the location of this shaft in relation to the movable coils L. l

Manipulation of the cam |01 by rotation of knob |09 to cause flange |02 to engage slot |03, places the inductive coupling adjustments M of the selectors 60 and 62 under control of the knob 1|. In this way the selectivitydn the intermediate-frequency portion of the system may be symmetrically expanded or contracted with respect to the intermediate frequency by axial displacement of knob 1| to'provide a desired selectivity for double sideband reception according to the operation of Fig. 3. p To insure that double sideband expansion will always be initiated from the tuning position, slide 04 is provided on its under side with a lip ||4 having a transverse slt ||5 atits extreme right. When the control knob 1| is in the tuning position, slot ||5 will be aligned with cam |01 to permit its rotation between stops |09 and 0 thereby to engage or disengage flange |02 with slot |03 as desired. For all double sideband expansions, however, disengagement of flange |02 from slide |04 is prevented by lip |4 bearing against cam |01 in its actuating position.

It must not be possible simultaneously to adjust the inductive couplings M and the capacitive couplings E. To insure this independence of controls, the travel of slide |04 is limited by bracket so that when the control knob 1| is pulled out for full double sideband expansion, pin 12 cannot engage the teeth of collar 11. The proper Shaft ||2 may be rigid limits of travel for slide |04 are determined by the dimensions s: and y between the ends of the slide and brackets in relation to the travel of pin 12 between collars 13 and 11./

If it is found desirable to terminate the selectors 90 and 92 with resistances P to maintain uniformity of response in the transmitted band, the adjusting arms of the resistances may be mechanlically coupled to shaft ||2 as indicated by the dashed lines ||9. In this way the terminating resistances of the selectors are varied simultaneously with andin opposite sense-to the inductive couplings M-and such as to assure the desired selectivity characteristic for each coupling adjustment for double sideband reception. As the inductive couplings are decreased for minimum coupling,'the resistances P are increased for maxsponse of curve a, Fig. 2, but not for the expanded single or double sideband selectivity adjustments.

This refinement in operation may in the system of Fig. 9 be effected by adjustment of the control knob II. To this end the rotary arms of switches ||1 and ||9 are mounted on the shaft 9| of the gang condenser E as indicated by the dashed connecting lines ||9. As shaft 9| is rotated. by knobli the arms of switches |1 and ||8 are rotated to connect resistors R across their respective condensers E, but only for their intermediate capacity settings at which condensers E in conjunction with the inductive couplings M provide the minimum total coupling between resonant circuits in accordance with curve a, Fig. 2. Since, moreover, resistances R must be disconnected for double as well as for single sideband expansions, the shunt paths through resistances R across condensers E are completed through contacts of switches |20 and |2| controlled by the adjustable arms of resistances P. The contacts are so arranged, as shown, that switches |20 and 2| will be closed only when the inductive couplings are adjusted by shaft ||2 for maximum selectivity as described.

denser |30, illustrated schematically. To this end,

shaft |3| supporting the rotor elements of the gang condenser assembly, is adjusted by a tuning lcontrol shaft |32 through a pulley |33, keyed to shaft |32, belt |34, and pulley |35 keyed to shaft |3|. The tuning operation is subject to control by a selectivity adjusting shaft |36, and can only occur when shaft |39 is adjusted to the tuning position for maximum intermediate-frequency selectivity as described below. When shaft |39 is properly adjusted for tuning, which is the position illustrated in the drawings, pin |31, extendingtransversely through shaft |39, pushes against a raised ball section |38 of a lever |39 which pivots on pin |40-, and thus moves the lever |39 away from a stop |4| against the pull of a spring |42, thereby causing idler rollers |43 to take out the Slack otherwise present in the tuning belt |34; so

continuously expanding said`resonance band unsymmetrically with respect to said carrier, thereby to select more of one sideband than of the other, said first and second means being adjustable to sharpen the tuning of said selector to said carrier frequency.

5. In a modulated carrier wave signaling system, a resonant band selector, said selector including xed and variable reactances, a first means for adjusting at least one of said variable reactancesto expand the resonance band of said selector symmetrically about the carrier fre- 'quency of a modulated carrier wave to select both of its sidebands equally, and a second means for adjusting at least -one other of said variable reactances for expanding said resonance band unsymmetrically with respect to said carrier frequency to select more of one sideband than of the other. Y

6. In a modulated carrier wave signaling system, a resonant band selector, said selector including fixed reactance elements, an adjustable mutual inductance and anadjustable condenser, a first means for adjusting said mutual inductance to expand the resonance band of said selector symmetrically about the carrier frequency of a modulated carrier wave to select both of its sidebands equally, and a second means for adjusting said condenser to expand said resonance band unsymmetrically with respect to said carrier frequency to select more of one sideband than of the other.

"7. In a modulated carrier wave signaling system, a, band selector including a pair of reactively coupled resonant circuits, a first means for adjusting the reactive coupling of said circuits in one sense to expand the resonance band of said selector symmetrically `about the carrier frequency of a modulated carrier wave thereby to select both of its sidebands equally, and a second 4' means for adjusting said reactive coupling in an opposite sense to expand said resonance band unsymmetrically with respect to said carrier frequency thereby to select more of one sideband than of the other.

8. An electric wave selector of the adjustable band-pass type including a pair of resonant circuits, adjustable opposing mutual and self-reactance couplings between said circuits, a rst means for adjusting said mutual reactance coupling to expand the frequency' band passed by` said selector symmetrically about a fixed mean frequency, and a second means for adjusting said self-reactance coupling to expand the frequency band passed by said selector unsymmetrically about said fixed frequency.

9. In a modulated carrier wave signaling system, a band selector including a pair of resonant circuits, adjustable opposing mutual and selfreactance couplings between said circuits, a first means for adjusting said mutual reactance coupling to expand the resonance band of said selector symmetrically about the carrier frequency of a modulated carrier wave to select both of its sidebands equally, and a second means for adjusting said self-reactance coupling to expand said resonance band unsymmetrically with reabout the carrier frequency of a modulated carrier wave to select both of its sidebands equally, and a second means for adjusting Vsaid capacitive coupling to expand said Lresonance band unsymmetrically with respect to said carrier frequency to select more of one sideband than of the other.

l1. In a modulated carrier wave signaling system, a resonant band selector, a first means for expanding the resonance band of said selector symmetrically aboutfthe carrier frequency of a modulated carrier wave to select both of its sidebands equally, and a second means for expanding said resonance band unsymmetrically with respect, to said carrier to select more of one sideband than of the other, and means for preventing the operation of either-of said expanding means except when the other of said expanding means is operated fully to contract said resonance band.

12. In a, modulated carrier wave signaling system, a resonant band selector, means for adjusting the selective properties of said selector in- ,nism in another degree of freedom for expanding said resonance band unsymmetrically with respect to said carrier thereby to select more of one sideband than of the other.

13. In a. modulated carrier Wave signaling system, a band selector comprising a pair of coupled resonant circuits, said selector including a .plu-

rality of adjustable coupling reactances, means including a control mechanism operable in at least two degrees of freedom, means responsive to operation of said control mechanism in one degree of freedom for adjusting at least oneof said reactances to expand the resonance band of said selector symmetrically with respect to the carrier frequency of a modulated carrier wave thereby to select `both of its sidebands equally, and means responsive to operation of said control mecha-v nism in another degree of freedom for adjusting at least one other of said reactances to expand said resonance band unsymmetrically with respect to said carrier thereby to select more of either of said sidebands than of the other.

14. In a modulated carrier wave signaling system, a resonant band selector, means for adjusting the selective properties of said selector includng a control shaft operable in at least two degrees of freedom comprising rotation and axial displacement, means responsive to operation of said control shaft in one of said degrees of freedom for expanding the resonance band of said selector symmetrically with respect to the carrier frequency of a modulated carrier wave, and means responsive -to operation of said control shaft in the other of said degrees of freedom for expandingsaid resonance band unsymmetrically with respect to said carrier frequency.

15. In a modulated carrier wave signaling system, a resonant band-selector, means for adjusting the selective properties of said selector includng a control shaft operable in at least two degrees of freedom comprising rotation and axial displacement, means responsive to axial displacement of said control shaft for expanding the resonance band of said selector symmetrically with respect to the carrier frequency'of a modudegrees of freedom comprising rotation and axial displacement, means responsive to operation of said control shaft'in one of said degrees of freedom for expanding the resonance band of said sevat lector symmetrically with respect to the carrier frequency of a modulated carrier wave, means responsive to operation of said control shaft in the other of said degrees of freedom for expanding said resonance band unsymmetrically with respect to said carrier frequency, and means including operating connections'betweensaid control shaft and said two expanding means whereby selective and mutually exclusive operation of either of said expanding means is provided.

17. In a modulated carrier wave signaling system, a resonant band selector, means for adjust-g ing the selective properties of said selector including a control shaft operable in at least two degrees of freedom comprising rotation and axial displacement, means responsive to operation of j said control shaft in one of said degrees of freedom for expanding the resonance band of said selector syn'nnetrically with respect to the carrier frequency of a modulated carrier wave, means responsive to'operation of said control shaft in the other of said degrees of freedom for expanding said vresonance band unsymmetrically with respect to saidcarrier frequency, and a clutch interconnecting said control shaft and thatv expanding means responsive to rotation thereof and disengageable upon axial displacement of said shaft to operate the other of said expanding means.

18. In a modulated carrier wave signaling system, a resonant band selector, means for adjusting the selective properties of said selector including a control shaft operable in at least two degrees of freedom comprising rotation and axial displacement, means responsive to operation of said control shaft in one of said degrees of freedom for expanding the resonance band of said selector symmetrically with respect to the carrier frequency of a modulated carrier wave, means responsive to operation of said control shaft in the other of said degrees of freedom for expanding said resonance band unsymmetricallyl with respect to saidy carrier frequency, and means responsive tov axial displacement of said control shaft for adjusting said expanding means responsive to rotation thereof to a predetermined normal setting.

19. In a modulated carrier wave signaling system, a resonant band selector, means for adjusting the selective properties of said selector including a control shaft operable in at least two degrees of freedom comprising rotation and axial displacement, meansresponsive to operation of' said control shaft in one of said degrees. of freedom forexpa'nding the resonance band of said selector symmetrically with respect t o the carrier frequency of a modulated carrier wave, means responsive to operation of said control shaft in the other of said degrees of freedom for expand- 'ing the resonance band of said selector unsymmetriealy with respect to the carrier frequency of a modulated carrier wave, and means associated with said control. shaftl for-preventing rotation thereof when axially displaced from a predetermined position.

' 20. In a modulated carriervwave signaling system, a resonant band selector, means for adjusting the selective properties of said selector including a control shaft operable in at least two degrees of freedom comprising rotation and axial displacement, means Aresponsive to operation of said control shaft in one of said degrees of freedom for expanding the resonance band of *said frequency of a modulated carrier wave, means responsive to operation of said control shaft in the other of said degrees of freedom for expanding the resonance band of said selector unsymmetrically with respect to the carrier frequency of a modulated carrier wave, a locking member supported from said control shaft, and guiding means for said member during axial displacement of said shaft, said guiding means being effective to restrain rotation of said shaft except when in a predetermined axial position.

21. In a modulated carrier wave signaling system, a signal-selecting and -translating circuit includingv a resonant band selector, means forl tuning said circuit to select a modulated carrier wave, means for expanding the resonance band of said selector symmetrically about the carrier frequency of the selected modulated waveto select both of its sidebands equally, and means for expanding said resonance balnd unsymmetrically with respect to said carrier to select more of one sideband than of the other. l

22. In a modulated carrier wave signaling system, a signal-selecting and translating circuit including a resonant band selector, means for tuning said'circuit to select a modulated carrier wave, means for expanding the resonance band of said selector symmetrically about the carrier frequency of the selected modulatedwave to select both 'of its sidebands equally, means for expanding said resonance band unsymmetrically with respect to said carrier to select more of one sideband than of the other, and a common control mechanism for said tuning means and both of said expanding means.

23. In a modulated carrier wave signaling system, a signal-selecting and -translating circuit including a resonant band selector, means for tuning said circuit to select a modulated carrier wave, meansfor expanding the resonance pand of said selector symmetrically about the carrier frequency of the selected modulated wave to 'select both of its sidebands equally, means for expanding said resonance band unsymmetrically with respect to said carrier to select more of one sideband than of the other, and a common control vmechanism for said tuning means and both of said expanding meansincluding provisions for selective and mutuallyexclusive operation of any thereof.

24. In a modulated carrierwave signaling system, a signal-selecting and -translating circuit including a resonant band selector, means for tuning said circuit to select a modulated carrierA l0 selector symmetrically with respect to the carrier p means for preventing operation of more than one of said `means simultaneously.

'25. Ina modulated carrier wave signaling system, a signal-selecting and -translating circuit including a resonant band selector, means for tuning said' circuit to select a modulated carrier -including a resonant band selector, means forl tuning saidcircuit toselect a modulated carrier wave, means for controlling the operation of said tuning means and for adjusting the selective .properties of said selector including a control mechanism operable in at least two degrees of freedom, means responsive to operation of said control mechanism in one degree of freedom for expanding the resonance band of said selector symmetrically about the carrier frequency of a selected modulated wave to select both of its sidebands equally, means responsive to operation oi.' said control mechanism in another degree of freedom for expanding said resonance band unsymmetrically with respect to said carrier to select more ofA one sideband than of the other, said control mechanism including provisions for t preventing operation of said tuning means except when' in a position corresponding to full contraction of said resonance band.

27. In a modulated can-ier wave signaling system, a tunable selector and a tuned band selector, means for adjusting the selective4 properties of said band selector including a control mechanism operable in at least two degrees of freedom, means responsive to operation of said control mechanism in one degree of freedom for expanding the resonance band'of said tuned selector symmetrically about the carrier frequency of a modulated carrier wave to select both of its sidebands equally, means responsive to operation of said control mechanism in another degree of freedom forV expanding said resonance band unsymmetrically with respect to said carrier Ito select more of onesideband than of the other, operation of' said control mechanism to a predetermined setting being effective to sharpen the tuning of said tuned selector to said carrier frequency, and means operative only-upon operation of said control mechanism to said predetermined setting for adjusting said tunable selector throughout a frequency range.

28. In a modulated carrier wave signaling system, a plurality of tunable selectors and a plurality of tuned band selectors, nfeans for adjusting the selective properties of said selectors including a control shaft operable. in two degrees of freedom comprising rotation and axial displacement, means responsive to rotation of said control shaft for expanding the resonance bands of said tuned selectors symmetrically about the carrier frequency of a modulated carrier wave to select both of its sidebands equally, mean responsive to axial displacement of said control shaft for expanding said resonance bands unsymmetrically with respect to said carrier frequency to select 7 more of one said sideband than of the other, op-

eration of said control shaft to a predetermined axial and rotational setting being effective to sharpen the timing o f said tuned selectors to said carrier frequency. and means operative only upon adjustment of said control shaft to said predetermined setting for adjusting 'said tunable selectors throughout a frequency rango.

29. In a modulated carrier wave signaling system, a tunable selector and a tuned band selector, means for adjusting the selective properties of said band selector including a rotatable'control shaft axially displaceable between limits, means responsive to displacement of said shaft to one of said limits for sharply tuning said tuned selector to the carrier frequency of a modulated carrier wave, and responsive to axial displacement of said shaft from said limit for expanding the resonance band of said tuned selector symmetrlcally about said carrier frequency for selecting both said bands equally, means responsive to rotation of said shaft at said limit for adjusting 'said tunable selector throughout a frequency range, and means responsive to rotation of said shaft at its opposite limit of axial displacement for expanding the resonance band of said tuned selector unsymmetrically with respect to said carrier to select more of one sideband than of the other.

30. In a modulated can'ier wave signaling system, a tunable selector and a tuned band selector, means for adjusting the selective properties ofsaid band selector including a rotatable control shaft axially displaceable between limits, means responsive to the displacement of said shaft to a certain angular setting at one of said limits for sharply tuning said tuned selectors to theV carrier frequency of a modulated carrier wave and responsive to rotation of said shaft at said limit for expanding the resonance band of said tuned selector unsymmetrically with respect to said carrier to select more of one sideband than of the other, means operative only for said setting of said shaft for adjusting said tunable selector throughout a frequency range, and means -responsive to axial displacement o; said shaft from said certain setting for expanding the resonance band of said tuned selector symmetrically about the carrier frequency to select both sidebands equally.

3l. In a superheterodyne modulated carrier wave receiving system, a plurality of tunable reception frequency selectors and tuned intermediste-frequency band selectors, means for adjusting the selective properties of said selectors including a control mechanism operable in at least two degrees of freedom, lmeans responsive Jto operation of said control mechanism in one degree of-freedom for expanding the resonance bands of said tuned selectors symmetrically about. the intermediate frequency to select both sidebands of a modulated carrier wave equally, means responsive to operation of said control mechanism in another degree of freedom for expanding said resonance bands unsymmetrically with respecteto said intermediate frequency tomeans ,for adjusting said resistance and for expanding the resonance band/[of said selector symmetrically about the carrier frequencyof a modulated carrier wave to select both of its sidebands equally while maintaining transmission reasonably uniform, within said band, and a second means for expanding said resonance band unsymmetrically with respect to said carrier fre- A quenoy to select more of one sideband than of the other.

33. In a modulated carrier wave signaling system, a band selector including a pair of resonant circuits, adjustable capacitive and inductive couplings between said circuits, an adjustable resistmeans being adjustable to sharpen the tuning of said selector to said carrier frequency.

34. In a modulated carrier wave signaling system, a band selector including a pair of resonant circuits, adjustable capacitive and inductivecouplings between said circuits, \a resistor, a first means for adjusting said inductive coupling' to expand the resonance band of said selector `sym-v metrically about the carrier frequency of a. modulated carrier wave to select both of its sidebands equally, a second means for adjusting said capacitive coupling to expand said resonance band unsymmetrically with respect to said carrier frequency to s elect more of one sideband than of the other, said rst and secondmeans being adjustable to predetermined settings to lis rierfrequency' to select more sharpen'the tuning of said selector to said carrier frequency, and means for connecting said resistor in shunt to said capacitive coupling only when both of said means are adjustedto said settings. f

35. In a modulated carrier tem, a bandselector including a pair of resonant circuits, said circuits being reactively coupled, and a reactance element coupling said circuits in opposition to said rst coupling, said lreactance elementbeing self-reactance adjustable between limits greater and less than that value whose coupling is equal and opposite to said first coupling to adjust the width of the band passed by said selector to a minimum about a frequency corresponding to the desired carrier wave and to expand the same'unsymmetrically about said carof either sideband than the other.

y 36. In a modulated carrier wave signaling system, a band selector including a pair of resonant circuits, a first reactance element couplingsaid pair of circuits in excess of optimum coupling,4

carrier wave and to expand the same unsymmetriwave signaling syscally about said carrier frequency to select more of either sideband than the other.'

37. In a. modulated carrier wave signaling system, a band selector including a-pair of resonantcircuits, said circuits being reactively coupled,

and means for adjusting the width of the resonance band of said selector and simultaneously adjusting the mean frequency thereof on either side of said carrier frequency comprising a reactance element coupling said circuits in opposition to said first coupling, said reactance ele- L ment beingrself-reactance adjustable between tance the coupling ofwhich is of Ythe order of f twice said first coupling to adjust the width of the band' passed by said selector tofa minimum about a frequency corresponding to the desired 4carrier wave,'and to expand the same unsymmetrically about said carrier frequency to select lmore of either sideband than of the other.

39. In a modulated carrier .wave signaling system, circuftaan inductive coupling between said circuits, and an adjustable condenser coupling said circuits in opposition to said inductive coupling, said condenser being adjustable between limits fgreater and less than that value whosecoupling is equal and opposite to said inductive coupling to adjust the width of the band passed by said selector to a minimum about a. frequency corre- A sponding-tothe desired carrier wave and to expand the same unsymmetrically about said carrier frequency to select mo're of either sideband than of the other.

40. In ka modulated carrier wave'signaling system, a band selector including a pair of resonant circuits, a shunt inductive coupling between said band selector including a pair of resonant circuits of over-optimum value, a` series capacitive coupling between said circuits acting in opposition to said inductive coupling, said capacitive coupling comprising an adjustable condenser having a maximum capacitance corresponding to a coupling of the order of twice that of said inductive coupling to adjust the width of the band passed by said selector to a minimum about a frequency corresponding tothe desired carrier wave and to expand the same unsymmetrically about said carrier frequency to select more of either sideband than of the other.

41. In a modulated carrier wave signali g system, a band selector including a pair of r pant circuits, a series inductive coupling between said circuits, a shunt capacitive coupling between said condenser adjustable between limits greater and less than that value whose coupling is equal and circuits, said capacitive coupling comprising a opposite to said inductive coupling to adjust the width of the band passed by said selector to a minimum about a frequency corresponding to, the desired carrier wave and to expand the same unsymmetrically about said carrier frequency to select more of eithersideband than of the other.

42. In a modulated carrier wave signaling system, a band selector including a pair of resonant circuits, a reactive coupling between said circuits actance element being a sell-reactance adjustable the other.

adjustable from a predetermined vvalue to adilrst coupling to adjust the width of said band just .the width ofthe resonance band of said seto a minimum about a frequency corresponding lector symmetrically about a frequency correto the desired carrier wave and to expand the sponding to the desired carrier wave, and a. resame unsymmetrlcally about said lcarrier freactance element coupling said circuits, said requency to select more o! either sideband than Vof I' between limits greater than and less than that JOHN F. FARRDWGTON. value whose coupling is equal and opposite to said 

